Aerodynamics Of Air-Permeable Multilayer Roof Cladding

Currently, design approaches to determine loads on different types of building cladding elements can vary significantly by product type, even though they may have similar geometries. Using the full-scale wind tunnel at the Insurance Institute for Business & Home Safety, external and net wind loads on two discontinuous metal roof systems were measured. The results indicate that cavity pressures in air-permeable multilayer cladding, such as discontinuous metal roofs are approximately uniform across individual panels and closely related across multiple panels which share the same cavity. The testing also showed that peak net loads tend to occur slightly after the peak spatial gradient of the external pressure across the cladding elements. The two types of discontinuous metal roofing products, which have significantly different cavity geometries, have similar ratios between the net and external wind loads with metal shingles having a Ceq value of 0.55 and metal panels having a Ceq value of 0.67. Overall, these experimental results indicate that the peak pressure equalization factor is dependent on the external pressure difference across the cladding, the geometry of the cladding, and the fluid inertia of the cavity flow. The experimental results also show that the peak pressure equalization factor is not dependent on location and wind direction, for panels that are not adjacent to the edges.